The Blues were looking to maintain the pressure on Premier League leaders Arsenal on Saturday but succumbed to a third away league loss of the season thanks to Oussama Assaidi's 90th-minute winner.
That defeat followed another away fixture in which Chelsea shipped three goals, although ultimately the London side were successful in a 4-3 triumph at Sunderland on Wednesday, but the England international concedes that the team must do more to eradicate errors or risk losing pace in the race for the title.
|6/5||Chelsea are 6/5 with BetVictor to win both halves against Steaua Bucharest|
"We talked about it after Sunderland and there were unfortunate incidents in the set-pieces, where we've had a look at it. Maybe it's just a bit of bad luck but, away from home, we've got to keep it tight. I feel we've done that most of the season but this result was poor for us.
"It's massively disappointing because it's so tight at the minute that you've got to keep chalking up results. A game which we felt we could have got points from, we've lost, which is very disappointing."
The defender particularly lamented Stoke's opening goal, when goalkeeper Petr Cech failed to deal with a Marko Arnautovic corner, allowing Peter Crouch to apply a close-range finish.
"We thought big Pete was going to come," he observed. "He didn't. I should have been tighter. All these little things ... of course, you can tidy up on mistakes but they're not major, major mistakes. They are just little bits and bobs which have happened in games this season and which I'm sure won't be happening in future."